1. Field of the Invention
The present invention relates to a display device, and more particularly to a routing wire disposed on a peripheral portion of a display region.
2. Description of the Related Art
A display device in the related art has a configuration where scanning signal lines (gate lines) extending in the X direction and arranged parallel to each other in the Y direction and image signal lines (drain lines) extending in the Y direction and arranged parallel to each other in the X direction are formed on a substrate; pixels formed by thin film transistors and pixel electrodes connected to corresponding thin film transistors are formed in a region surrounded by the scanning signal lines and the image signal lines; and plural pixels are arranged in a matrix in a display region. In the display device with such a configuration, a scanning signal line driving circuit for supplying scanning signals (gate signals) to the scanning signal lines, an image signal line driving circuit for supplying image signals to the image signal lines, and the like are disposed on side portions of the substrate. The driving circuits, the scanning signal lines, and the image signal lines are electrically connected to each other by routing wires formed at a so-called bezel region between the display region and the end portions of the substrate.
It is known that occurrence of signal delays or the like in the scanning signal lines, the image signal lines, and the routing wires has great influence on display quality, and they are formed using metal thin films in order to suppress the occurrence of signal delays or the like as much as possible. In the display device using the metal thin films, as in a liquid crystal display of the IPS type, the scanning signal lines and the routing wires are formed in different processes, and the scanning signal lines and the routing wires are electrically connected to each other by providing contact holes overlapping the respective wires on an insulating layer formed to be an upper layer of the scanning signal lines and the routing wires and by providing a transparent conductive film to be an upper layer of the insulating layer (for example, refer to U.S. Pat. No. 5,621,556).
However, in the display device in the related art, a region (connection region) where the contact holes for electrically connecting the scanning signal lines to the routing wires are formed is generally formed in the bezel region in consideration of the influence on display quality. In the bezel region, as shown in FIG. 11A which is a plan view illustrating a connection region and FIG. 11B which is a cross-sectional view taken along the line XIB-XIB in FIG. 11A, in a region where an end portion of a scanning signal line DCR and an end portion of a routing wire GAL formed on a surface of a first substrate SUB1 are close to each other, a first connection hole (first contact hole) TH1 is formed in a first insulating layer PAS1 which is formed to be an upper layer of the routing wire GAL, and a second connection hole (second contact hole) TH2 is formed in the first insulating layer PAS1 and the second insulating layer PAS2 sequentially formed to be an upper layer of the scanning signal line DCR. In the connection region, for example, a transparent conductive film CHL is formed to be an upper layer of the second insulating layer PAS2 so as to cover the first connection hole TH1 and the second connection hole TH2, for example, in a process of forming pixel electrodes, and the scanning signal line DCR is electrically connected to the routing wire GAL via the transparent conductive film CHL.
In the display device having the configuration, as shown in FIGS. 11A and 11B, the end portion of the transparent conductive film CHL is open on the second insulating layer PAS2. For this reason, as shown in FIG. 11B, in a case where an impurity such as moisture permeates through the interface between the second insulating layer PAS2 and the transparent conductive film CHL as indicated by the arrow N, the permeating impurity such as moisture reaches the first connection hole TH1 along the interface between the second insulating layer PAS2 functioning as a planarization film and the transparent conductive film CHL, then further permeates along the side wall surface thereof, and easily reaches a connection region P between the transparent conductive film CHL and the routing wire GAL. Therefore, there is concern that the impurity may corrode the routing wire GAL formed of a metal thin film, and thus a signal line from the scanning signal driving circuit to the scanning signal line DCR via the routing wire GAL may be disconnected.
Particularly, since thermal expansion coefficients of the metal thin film and the first and second insulating layers PAS1 and PAS2 are different from those of the transparent conductive film CHL and thus there is a higher possibility that foreign matter (impurities) such as moisture may permeate, countermeasures thereof are in considerable demand.
The present invention is made in consideration of these problems, and an object of the present invention is to provide a technique which prevents foreign matter such as moisture from permeating through an interface between a transparent conductive film and an underlying insulating film so as to improve the reliability of a connection region of signal lines, thereby improving reliability of a display device.